Microbial biotransformation of aryl sulfanylpentafluorides

We report, for the first time, the biotransformation of potential pollutants bearing the pentafluorosulfanyl (SF₅-) functional group in a fungus and bacteria. Cunninghamella elegans transformed p-methoxy phenyl SF₅ via demethylation; Pseudomonas knackmussii and P. pseudoalcaligenes KF707 transformed amino-, hydroxyamino- and diamino- substituted phenyl SF₅, forming the N-acetylated derivatives as the main product. Cell-free extract of Streptomyces griseus transformed 4-amino-3-hydroxy-phenyl SF₅ to the N-acetylated derivative in the presence of acetyl CoA, confirming that an N-acetyltransferase is responsible for the bacterial biotransformations. Approximately 25 % of drugs and 30 % of agrochemicals contain fluorine, and the trifluoromethyl group is a prominent feature of many of these since it improves lipophilicity and stability. The pentafluorosulfanyl substituent is seen as an improvement on the trifluoromethyl group and research efforts are underway to develop synthetic methods to incorporate this moiety into biologically active compounds. It is important to determine the potential environmental impact of these compounds, including the potential biotransformation reactions that may occur when they are exposed to microorganisms.     

Particulate Loads Caused by Wind Erosion in the Great Plains

Dust is always present in the air, but when wind erosion occurs, both the flux of soil particles into the air and the particulate concentration increase by orders of magnitude. Previous research¹ indicated that median duststorm concentration was 4.85 mg/m³ and median annual hours with duststorms was 45 in the Great Plains during the 1950’s. Of the total soil moved by wind, the suspended particulates probably represent 10% or less.²-³     

Transport of Escherichia coli through variably saturated sand columns and modeling approaches

A sand column leaching system with well-controlled suction and flow rate was built to investigate the effects on bacterial transport of air-water interface effects (AWI) correlated to water content, particle size, and column length. Adsorption of Escherichia coli strain D to silica sands was measured in batch tests. The average % adsorption for coarse and fine sands was 45.9+/-7.8% and 96.9+/-3.2%, respectively. However, results from static batch adsorption experiments have limited applicability to dynamic bacterial transport in columns. The early breakthrough of E. coli relative to bromide was clear for all columns, namely c. 0.15 to 0.3 pore volume earlier. Column length had no significant effects on the E. coli peak concentration or on total recovery in leachate, indicating retention in the top layer of sands. Tailing of breakthrough curves was more prominent for all fine sand columns than their coarse sand counterparts. Bacterial recovery in leachate from coarse and saturated sand columns was significantly higher than from fine and unsaturated columns. Observed data were fitted by the convection-dispersion model, amended for one-site and two-site adsorption to particles, and for air-water interface (AWI) adsorption. Among all models, the two-site+AWI model achieved consistently high model efficiency for all experiments. Thus it is evident from experimental and modeling results that AWI adsorption plays an important role in E. coli transport in sand columns.     

Allocating cleanup costs among potentially responsible parties

Allocating costs for hazardous waste site cleanup among potentially responsible parties is unique to the specific circumstances, history, and data for the site. As such, distinct technical approaches are often needed considering the Gore and Torres factors to develop an overall allocation. These factors include both technical and nontechnical considerations that the trier of fact must weigh to arrive at the overall allocation. This article reviews the legal and technical framework in allocating cleanup costs at hazardous waste sites and presents several case histories illustrating the integration of fact, science and law in the final allocation.     

Evaluation of performance reference compounds in polyethylene-based passive air samplers

Polyethylene-based passive air samplers (PSDs) were loaded with performance reference compounds (PRCs) and deployed in a wind tunnel to examine the effects of wind speed on sampler performance. PRCs could be loaded reproducibly into PSDs, with coefficients of variation only exceeding 20% for the more volatile compounds. When PSDs were exposed to low (0.5-1.5 m s-1) and high (3.5-4.5 m s-1) wind speeds, PRC loss rate constants generally increased with increasing wind speed and decreased with increasing sampler/air partition coefficients. PSD-based air concentrations calculated using PRC loss rate constants and sampler/air partition coefficients and air concentrations measured using active samplers compared closely. PRCs can be used to account for the effect of differences in wind speeds on sampler performance and measure air concentrations with reasonable accuracy.     

Nestmate recognition in social insects: overcoming physiological constraints with collective decision making

Social insects rank among the most abundant and influential terrestrial organisms. The key to their success is their ability to form tightly knit social groups that perform work cooperatively, and effectively exclude non-members from the colony. An extensive body of research, both empirical and theoretical, has explored how optimal acceptance thresholds could evolve in individuals, driven by the twin costs of inappropriately rejecting true nestmates and erroneously accepting individuals from foreign colonies. Here, in contrast, we use agent-based modeling to show that strong nestmate recognition by individuals is often unnecessary. Instead, highly effective nestmate recognition can arise as a colony-level property from a collective of individually poor recognizers. Essentially, although an intruder can get by one defender when their odor cues are similar, it is nearly impossible to get past many defenders if there is the slightest difference in cues. The results of our models match observed rejection rates in studies of ants, wasps, and bees. We also show that previous research in support of the optimal threshold theory approach to the problem of nestmate recognition can be alternatively viewed as evidence in favor of the collective formation of a selectively permeable barrier that allows in nestmates (at a significant cost) while rejecting non-nestmates. Finally, this work shows that nestmate recognition has a stronger task allocation component than previously thought, as colonies can nearly always achieve perfect nestmate recognition if it is cost effective for them to do so at the colony level.